To digitize a film for signal processing, transmission, or storage, the film is advanced frame by frame past an optical scanner. The thin film material must be kept flat within the depth of focus of the optical system in order to assure accurate pickup of the image on the film. The required flatness may be a few micrometers, which is particularly difficult when dealing with the thin, flexible films typically used for photographic imaging. For example, when mounted between two sprockets, 35 mm movie film tends to stretch into a cylindrical shape in the unsupported region between the holding sprockets. Therefore, it has become necessary to utilize additional means for flattening the film while it passes by the optical scanner.
One method for maintaining the planarity of film during scanning is to place the film material under a flat plate of transparent material, such as glass. A disadvantage to this method is that the transparent plate adds another optical element between the film and the scanning system, which can introduce errors in addition to interfering with the illumination during scanning.
An alternative film flattening technique has been to pass the film material through a frame which contacts the periphery of the film image area and has an open window through which the film image can be scanned. While the open window area avoids the problems of lighting alteration and of introducing artifacts to the scanned film image, optimal film flatness cannot be realized with only peripheral film contact. Both of the foregoing solutions require that additional time be spent in advancing the film and aligning the film image to the plate or window between scans. In addition, the prior art solutions both introduce new sources of error since physical elements of the system are contacting the film as it advances, which could lead to scratching or tearing of the film material.
It is therefore an objective of the present invention to provide a method and system for optimizing film flatness during scanning.
It is another objective of the invention to provide a system and method for achieving optimal film flatness without introducing additional optical elements as possible sources of error to the scanning system.
Yet another objective of the invention is to provide a system which allows scanning of film to be conducted continually, without the need to regularly stop the scanning process in order to advance and align the film.
Still another objective of the invention is to provide a system and method for film scanning which does not damage the film during the scanning process.